Heat pump system



June 1963 D. VAN DEN BERGE ETAL HEAT PUMP SYSTEM Filed Oct. 31. 1961 I NV E N T 0 R S D E N B E R G T G. M l N E m 0 O o 2 A T T O R N E Y SUnited States Patent 3,091,944 HEAT PUMP SYSTEM Dick Van Den Barge andRobert G. Miner, both of La Crosse, Wis, assignors to The Trane Company,La Crosse, Win, a corporation of Wisconsin Filed Oct. 31, 1961, Ser. No.149,076 4 Claims. (Cl. 6ZP-197) This invention relates generally to aheat pump refrigcrating system and more particularly to a heat pumpretrigeration system which incorporates a high side pressure controlwhen the temperature of the coolant passing over the heat exchangeracting as a condenser is below that necessary for proper operation ofthe expansion means.

In recent years, the air conditioning industry has had serious problemsin the use of air conditioning equipment Where the temperature of thecooling fluid, employed as the heat absorbing medium for the heatexchanger acting as a condenser, is abnormally low. The employment ofsuch low temperature heat absorbing medium results in a drop in highside pressure below a predetermined level causing a reduction in theuseful capacity of the heat exchanger acting 'as an evaporator due toinadequate operating pressures at the expansion means. The solution tothe problem naturally entails raising or maintaining the high sidepressure. Basically, this is done by flooding or reducing theeffectiveness of the heat exchanger acting as a condenser when the highside pressure falls below a predetermined minimum.

In the normal heat pump operation employing air [on both the heatexchangers the above problem is prevalent on both the heating andcooling cycles. On the cooling cycle when the temperature of thecondensing medium is below that desired the evaporator does not performthe cooling performance required to maintain proper comfort conditionsin the conditioned space. On the heating cycle the heat exchange mediumbeing heated by the heat exchanger acting as a condenser is normally ofa very low temperature causing insufiicient pressure at the expansionmeans resulting in premature icing of the heat exchanger acting as anevaporator and in stopping of the compressor on low pressure cut-out dueto low suction pressure.

It is, therefore, an object of the invention to provide automaticcontrol of the head or high side pressure in a heat pump system byflooding the heat exchanger acting as a condenser in response to highside pressures.

Another object of the invention is to provide a hot gas bypass conduitfiom the compressor discharge line to the liquid line between thecondenser and receiver and to provide pressure responsive means in thebypass conduit and in the condenser outlet conduit to control theeffective condensing surface of the condenser.

A third object of the invention is to provide a heat pump refrigerationcycle with a hot gas bypass conduit extending from the compressordischarge line to the liquid line and bypassing the condenser a'nd toprovide a pressure responsive valve at the junction of the hot ga bypassconduit and the liquid line to automatically maintain the proper highside pressure at low ambient coolant temperatures.

A still further object of the invention is to provide a heat pumprefrigeration cycle with hot gas bypass conduit from the compressordischarge line to the liquid line and bypassing the condenser and toprovide pressure responsive valves in the hot gas bypass conduit and inthe liquid line between the condenser and the junction of the bypassconduit and the liquid line to control the high side pressure.

Other objects and advantages of the invention will be 3,091,944 PatentedJune 4, 1963 clearly apparent as the specification proceeds to describethe invention with reference to the accompanying drawings in which:

FIGURE 1 is a schematic representation of a refrigeration systemincorporating the invention in the preferred embodiment; and

FIGURE 2 schematically represents another form of the invention.

FIGURE 1 shows the preferred embodiment of the in,- vention incorporatedin a refrigeration system including a compressor 10, an outdoor heatexchanger 12, a receiver 14, expansion means 16 and 17, and an indoorheat exchanger 18. Expansion means 16 and 17 are shown as expansionvalves responsive to suction, but obviously other expansion devices maybe used without departing from the scope of the invention. A tour vvayreversing valve 20 of any conventional construction is connected betweenthe heat exchangers 18 land 12. A high pressure cut-out 22 is connectedto discharge line 24 to stop the compressor 10 in case of unusually highdischarge pressures. A low pressure cut-out 26 is connected to suctionconduit 28 to stop the operation of compressor 10 in case of unusuallylow suction pressures.

On the normal cooling cycle hot uncondensed refrigerant will passthrough conduit 24, reversing valve 20, conduit 30 to the outdoor heatexchanger 12 :and be condensed therein. Liquid refrigerant from heatexchanger 12 will then flow to receiver 14 through conduits 32 and 34,check valve 36, conduits 38 and 4-0, and three Way pressure responsivevalve 42. From receiver 14 liquid refrigerant flows through conduit 44,check valve 46', conduit 48, expands through expansion valve 16, passesthrough conduits 5i and 52, absorbs heat from the air to be conditionedin the indoor heat exchanger 18 and returns to the compressor 10 throughconduit 54, reversing valve 20, and conduit 28. On the normal heatingcycle, the position of reversing valve 2b is reversed and hotuncondensed refrigerant is delivered to indoor heat exchanger 18 throughconduits 24 and 54 where the refrigerant is condensed and gives up heatto the heat exchange medium passing through the heat exchanger.Condensed refrigerant then flows to receiver 14 through conduit 52,check valve 56, conduits 53 and 4t), and three way pressure responsivevalve 42. Liquid refrigerant from the receiver flows through conduit6i), check valve 62, conduit 64, expands through expansion valve 17 andpasses into the outdoor heat exchanger 12 via conduitsds and 32 whereinit absorbs heat from the heat exchange medium passing over the heatexchanger. The vaporized refiriger-ant is then returned to thecompressor via conduit 3%, reversing valve 20, and suction conduit 28.

Three way pressure responsive valve 42 consists of casing 70, inlet port72 connected to hot gas bypass line 74, inlet port 76 connected toliquid line 40, and outlet port 78 connected to receiver 14. A flexiblediaphragm 89 of metal or other suitable material is secured to casing 70and moves valve head 82 between valve ports 84 and 86, depending on thepressure in chamber 88 acting against the force of spring WP. Screwmember 92 is provided for adjustment of the compression of spring 90.

Under either the normal heating or cooling operation of our improvedheat pump cycle when the heat exchange medium passing over the heatexchanger acting as a condenser is above a predetermined minimumtemperature, 'hot uncondensed refrigerant will pass through conduit 74into chamber 88 of pressure responsive valve 42 and act againstdiaphragm '80 and spring 90 to move valve head 82 to the left andthereby close valve port 84 and open port 86. As described hereinbeforethe liquid refrigerant from either indoor heat exchanger 12 Assume fordiscussion purposes that the heat exchange medium passing over theindoor heat exchanger 18 is primarily air recirculated from the areabeing conditioued and the heat exchange medium passing over the outdoorheat exchanger is ambient air. It can readily be seen that when therefrigeration system is in operation on the normal cooling cycle therewill be periods when the ambient air temperature will be lower than thatrequired for proper condensing. This naturally will result in reducedpressure at the expansion valve IG'the-reby reducing the effectivecapacity of the heat exchanger 18. Conversely, when the refrigerationsystem is operating on the heating cycle, a problem is encountered onstart-up since the recirculated air is cooler than desired resulting inreduced condensing temperatures across the indoor heat exchanger causingreduced effectiveness of the outdoor heat exchanger 12. This reducedeffectiveness of the outdoor heat exchanger 12 resulting in cutting offthe compressor on low pressure cut-out and constant reversing of therefrigeration cycle to defrost the outside heat exchanger 12 because ofpremature icing. Both the cutting out of the compressor and constantreversing of the reversing valve result in excessive wear on thecomponents of the system and very slow heating of the space to beconditioned. Our improved heat pump refrigeration cycle provides highside pressure control on both the heating and cooling cycles toalleviate the above mentioned problems.

As indicated above, control of head pressure is necessary on both theheating and cooling cycles. Our new and improved high side pressurecontrol is effective on both the heating and cooling cycles. Basicallyour control will flood the outdoor heat exchanger 12 on cool ing whenthe ambient air temperature is below a predetermined minimum or willflood the indoor heat exchanger 18 on the heating cycle when therecirculated air temperature is below a predetermined minimum.

Operation-FIGURE 1 Assuming that either one or the other of the aboveadverse conditions exist and control of high side pressure is necessary,the refrigeration system will automatically flood the heat exchangeracting as a condenser. Due to one or the other of the above mentionedadverse conditions the high side pressure will be reduced causing areduction of operating pressure at either expansion valve 16 orexpansion valve 17 depending on whether the system is heating orcooling. The pressure in hot gas bypass 74 will also be reduced and thespring 90 in conjunction with the diagram 80 will move valve head 82 tothe right, opening valve port 84 and throttling valve port 86. This hasa twofold effect on the system. First, liquid will back up in the heatexchanger acting as a condenser decreasing the effective condensingsurface and causing an increase in head pressure. This is accomplishedsince little or no liquid can flow to the receiver 14 through conduit 40because of the throttling effect of valve head 82 on valve port 86 ofthree way valve 42. Therefore the liquid condensed in the heat exchangeracting as a condenser will accumulate in the heat exchanger causing thehead pressure to build up. Secondly, hot gas from the bypass 74 willpass into the receiver 14 by way of valve port 84- and thereby warm therefrigerant in the receiver causing an increase in pressure which istransmitted to the expansion valve connected to the heat exchangeracting as an evaporator. During periods when low temperature air ispassing over the heat exchanger acting as a condenser the valve 42modulates so that the system substantially reaches an equilibrium atwhich the high side pressure is satisfactory for proper operation of theexpansion means. When the high or normal temperature air is passing overthe heat exchanger acting as a condenser, the high side pressure willincrease to the proper operating pressure and valve port 84 will beclosed by the pressure transmitted to chamber 88 by conduit 74 and theliquid from the heat exchanger acting as a condenser will pass into thereceiver 14 and the system will resume normal operation.

Modification 0 FIGURE 2 Looking now to FIGURE 2, there is shown amodified form of the invention. The basic refrigerant components shownin FIGURE 1 will be denoted by the same reference numbers in FIGURE 2.Instead of having a single three Way pressure responsive valve connectedto the hot gas bypass conduit 74 and to the liquid line 40, I haveprovided a pressure regulating valve 94 in the hot gas bypass conduit 74and a back pressure valve 96 in the liquid line 40.

Pressure regulating valve 94 and back pressure valve 96 are similar inconstruction in that each valve has a casing 98, a diaphragm 100 securedto the casing 98, a spring 10-2 with adjusting nut 104 exerting pressureon diaphragm 100, valve stem 106 attached to the diaphragm 100, and witha valve head 108 attached .to valve stem 106. Valve 94 differs fromvalve 96 in that a rise in pressure will close valve 94 but will openvalve 96. This is accomplished by locating the valve head 108 of valve94 on the outlet side of the valve port 110. Note valve 96 where thevalve head 108 is on the inlet side of valve port 112.

In normal operation when the air temperature is sufficiently high tomaintain proper operating pressures, the discharge pressure will act ondiaphragm 100 of pressure regulating valve 94 and maintain valve head108 against valve port 110- to shut off the passage of hot gas from theconduit 74 to the receiver 14. At the same time, the pressure in theliquid line 40 will act on the diaphragm 100 of back pressure valve 96to maintain the valve head 108 away from the port 112 against the actionof the spring 102. To refrigerant will pass consecutively throughdischarge conduit 24, the heat exchanger acting as a condenser, backpressure valve 96, receiver 14, expansion valve, heat exchanger actingas an evaporator, and back to the compressor 10 through suction line 28.

As the high side or head pressure decreases, the diaphragm of valve 94will start to open valve port 110 by moving valve head 108 to the right.If the high side pressure continues to decrease, the valve head 108 ofvalve 94 will move to a position where valve port 110' is completelyopen. The tensions on springs 102 are set so that the pressureregulating valve 94 will open completely on decreasing pressure and thenafter a further decrease of pressure, the back pressure valve 96 willstart to close. As in the modification of FIGURE 1, back pressure valve96 will throttle the conduit 40 which provides communication between theheat exchangers and the receiver, when the head pressure is low. Thiswill cause condensed liquid to back up in the heat exchanger acting as acondenser. This modification is completely automatic and is operateddirectly from the pressures in the system in order to flood thecondenser in accordance with the high side. pressure drop. On increasingpressure, the above operation will be reversed and the back pressurevalve 96 will be completely open before the pressure regulating valve 94starts to close.

It can readily be seen that we have provided a new and improved highside pressure control for heat pump systems which automatically reactsto a drop in head pressure to partially or completely flood the heatexchanger acting as a. condenser. Such control provides proper operatingtemperatures and pressures when operating on the cooling cycle with lowambient air conditions surrounding the heat exchanger acting as acondenser. Our

system further eliminates on the heating cycle premature icing of theheat exchanger acting as an evaporator and eliminates unnecessary Wearon the compressor due to excessive starting and stopping of thecompressor on low pressure cut-out.

Looking further at our new and novel head pressure control for heat pumpsystems, it is obvious that we have provided a control which iscomparatively small in size, easy and inexpensive to manufacture, andgives positive control of the flooding of the heat exchanger acting as acondenser. Note that in both forms of the invention during conditions ofhigh air temperaure, the hot gas bypass is positively closed, and thatthe compressor discharge pressure acts directly on the held up liquid inthe heat exchanger acting as a condenser to force the liquid out of theheat exchanger and allows it to operate at full capacity.

Although we have described in detail the preferred embodiments of ourinvention, we contemplate that many changes may be made withoutdeparting from the scope or spirit of our invention, and we desire to belimited only by the claims.

We claim:

1. A reversible cycle refrigeration system comprising: an indoor heatexchanger, an outdoor heat exchanger, conduit means for carrying liquidrefrigerant connecting said indoor heat exchanger to said outdoor heatexchanger, expansion means operably associated with said heatexchangers, a compressor having a suction line and a discharge line,reversing means connected to said discharge and suction lines toreversibly connect said discharge and suction line to said heatexchangers for effecting flow of refrigerant through said system ineither direction whereby said system may be operated on a cooling cyclewith the outdoor coil functioning as a condenser or on a heating cyclewith the outdoor coil functioning as a condenser or on a heating cyclewith the indoor coil functioning as a condenser, a hot gas bypass lineconnected to said discharge line, and automatic pressure responsivevalve means connected to said conduit means and said hot gas bypass lineto restrict the flow of refrigerant from said indoor heat exchanger whenthe system is operating on the heating cycle and the temperature of theheat exchange medium passing through said indoor heat exchanger is belowa predetermined minimum and to restrict the flow of refrigerant fromsaid outdoor heat exchanger when the system is operating in the coolingcycle and the temperature of the heat exchange medium passing throughsaid outdoor heat exchanger is below a predetermined minimum.

2. A reversible cycle refrigeration system comprising: an indoor heatexchanger, an outdoor heat exchanger, conduit means for carrying liquidrefrigerant connecting said indoor heat exchanger to said outdoor heatexchanger, a receiver connected to said conduit means, expansion meansoperably associated with said heat exchangers, a compressor having asuction line and a discharge line, reversing means connected to saiddischarge and suction lines to reversibly connect said discharge andsuction line to said heat exchangers for effecting flow of refrigerantthrough said system in either direction whereby said system may beoperated on a cooling cycle with the outdoor coil functioning as acondenser or on a heating cycle with the indoor coil functioning as acondenser, a hot gas bypass line connected to said discharge line, andautomatic pressure responsive valve means connected to said receiver,said conduit means, and said hot gas bypass line to restrict the flow ofrefrigerant from said indoor heat exchanger when the system is operatingon the heating cycle and the temperature of the heat exchange mediumpassing through said indoor heat exchanger is below a predeterminedminimum and to restrict the flow of refrigerant from said outdoor heatexchanger when the system is operating in the cooling cycle and thetemperature of the heat exchange medium passing through said outdoorheat exchanger is below a predetermined minimum.

3. The structure of claim 2 wherein said automatic pressure responsivevalve means is a three way pressure controlled valve with one portconnected to said hot gas bypass line, a second port connected to saidconduit means, and a third port in communication with said receiver.

4. The structure of claim 3 wherein said automatic pressure responsivevalve means is :a pressure regulating valve in said hot gas bypass lineand a back pressure valve in said conduit means.

References Cited in the file of this patent UNITED STATES PATENTS2,874,550 Musson Feb. 24, 1959 2,954,681 McCormack Oct. 4, 19602,976,696 Rhea Mar. 28, 1961

1. A REVERSIBLE CYCLE REFRIGERATION SYSTEM COMPRISING: AN INDOOR HEAT EXCHANGER, AN OUTDOOR HEAT EXCHANGER, CONDUIT MEANS FOR CARRYING LIQUID REFRIGERANT CONNECTING SAID INDOOR HEAT EXCHANGER TO SAID OUTDOOR HEAT EXCHANGER, EXPANSION MEANS OPERABLY ASSOCIATED WITH SAID HEAT EXCHANGERS, A COMPRESSOR HAVING A SUCTION LINE AND A DISCHARGE LINE, REVERSING MEANS CONNECTED TO SAID DISCHARGE AND SUCTION LINE TO REVERSIBLY CONNECT SAID DISCHARGE AND SUCTION LINE TO SAID HEAT EXCHANGERS FOR EFFECTING FLOW OF REFRIGERANT THROUGH SAID SYSTEM IN EITHER DIRECTION WHEREBY SAID SYSTEM MAY BE OPERATED ON A COOLING CYCLE WITH THE OUTDOOR COIL FUNCTIONING AS A CONDENSER OR ON A HEATING CYCLE WITH THE OUTDOOR COIL FUNCITONING AS A CONDENSER OR ON A HEATING CYCLE WITH THE INDOOR COIL FUNCTIONING AS A CONDENSER, A HOT GAS BYPASS LINE CONNECTED TO SAID DISCHARGE LINE, AND AUTOMATIC PRESSURE RESPONSIVE VALVE MEANS CONNECTED TO SAID CONDUIT MEANS AND SAID HOT GAS BYPASS LINE TO RESTRICT THE FLOW OF REFRIGERANT FROM SAID INDOOR HEAT EXCHANGER WHEN THE SYSTEM IS OPERATING ON THE HEATING CYCLE AND THE TEMPERATURE OF THE HEAT EXCHANGE MEDIUM PASSING THROUGH SAID INDOOR HEAT EXCHANGER IS BELOW A PREDETERMINED MINIMUM AND TO RESTRICT THE FLOW OF REFRIGERANT FROM SAID OUTDOOR HEAT EXCHANGER WHEN THE SYSTEM IS OPERATING IN THE COOLING CYCLE AND THE TEMPERATURE OF THE HEAT EXCHANGE MEDIUM PASSING THROUGH SAID OUTDOOR HEAT EXCHANGER IS BELOW A PREDETERMINED MINIMUM. 